TY - JOUR T1 - Multiple Modes of RyR2 Inhibition by Flecainide JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.114.094623 SP - mol.114.094623 AU - Divya Mehra AU - Mohammad S Imtiaz AU - Dirk F vanHelden AU - Bjorn C Knollmann AU - Derek R Laver Y1 - 2014/10/01 UR - http://molpharm.aspetjournals.org/content/early/2014/10/01/mol.114.094623.abstract N2 - Catecholaminergic polymorphic ventricular tachycardia (CPVT) causes sudden cardiac death due to mutations in cardiac ryanodine receptors (RyR2), calsequestrin or calmodulin. Flecainide, a Class I anti arrhythmic drug, inhibits RyR2 and prevents CPVT. The purpose of this study is to identify inhibitory mechanisms of flecainide on RyR2. RyR2 were isolated from sheep heart, incorporated into lipid bilayers and investigated by single channel recording under various activating conditions including the presence of cytoplasmic ATP (2 mM) and a range of cytoplasmic [Ca2+], [Mg2+], pH and [caffeine]. Flecainide applied to either the cytoplasmic or luminal sides of the membrane inhibited RyR2 by two distinct modes: 1) a fast block consisting of brief substate and closed events with mean duration of ~ 1 ms, and 2) a slow block consisting of closed events with a mean duration of ~ 1 s. Both inhibition modes were alleviated by increasing cytoplasmic pH from 7.4 to 9.5 but were unaffected by luminal pH. The slow block was potentiated in RyR2 channels that had relatively low open probability whereas the fast block was unaffected by RyR2 activation. These results show that flecainide has two independent mechanisms for RyR2 inhibition, both having a cytoplasmic site of action. The slow mode is a closed channel block whereas the fast mode blocks independent of RyR2 open state. ER -